1) To prepare gingerbread cookies: cream butter and sugar in the bowl of a stand mixer until fluffy. Add spices, egg and molasses; mix to blend. Combine dry ingredients in a separate bowl; slowly add to mixing bowl on low speed until fully blended. Pat dough into 2 cookie dough disks. Cover and chill for 1 hour.
2) Preheat oven to 350 degrees F.
3) Roll 1 cookie dough disk out on a floured surface to ⅛-to ¼-inch thick, lifting and turning dough as you roll (reserve remaining cookie dough for another use). Cut out shapes with comet/shooting star-shaped cookie cutter. Transfer to baking sheets lined with parchment. Bake for 8 to 10 minutes, or until slightly light brown around outer edges. Cool.
4) To prepare frosting: combine cream cheese and butter in bowl of stand mixer and mix until fully blended. Slowly add powdered sugar until blended; add vanilla and orange zest and mix until smooth and creamy.
5) Pipe royal icing around outer edges of cookies, if desired.
6) Frost cupcakes with offset spatula or piping bag. Sprinkle sparkling sugar over frosting and top each cupcake with a gingerbread comet cookie.